1. Field of the Invention
The present invention relates to an electron beam apparatus capable of monitoring at high-resolution.
2. Description of Related Art
For example, in order to perform inspection or observation of the shape of a fine pattern electronic device, conventionally, various electron beam devices such as scanning electron microscopes etc. have been used, and in particular, there has been a high demand for high resolution observation as a result of electronic devices becoming ultra fine in recent years. In Japanese Patent Laid-open Publication No. 2001-185066, there is proposed an electron beam apparatus capable of high-resolution observation provided with an electromagnetic field compound lens capable of applying a negative potential to both a magnetic pole close to a sample for the magnetic lens and to the sample.
It is well-known that a chromatic aberration coefficient Cc becomes large as the distance between the position of an electrically insulating member such as ceramic etc. and the tip of a magnetic pole applying a potential, i.e. as the distance between the position of the electrically insulating member and the surface facing the sample, becomes larger. With the electromagnetic field compound lens of the electron beam apparatus proposed in Japanese Laid-open Publication No. 2001-185066, electrically insulating material for maintaining a high-voltage at tapered magnetic pole tips is provided at a position away from a surface facing the sample of the magnetic poles. The distance between the position of the electrically insulating member of ceramic etc. and the surface facing the sample of the magnetic pole is therefore substantial, and the chromatic aberration coefficient Cc is therefore large. Providing electrical insulating material in order to prevent charging by the electron beam in the vicinity of the opposing surface of the sample for the magnetic pole close to the sample is spatially difficult. Magnetic flux therefore leaks into a magnetic gap due to the electrically insulating member and a sub-lens magnetic field therefore exists displaced from a main lens magnetic field on the optical axis. This is therefore detrimental to image resolution at low acceleration voltages.
In order to resolve these problems, in a further practical example, there is proposed in Japanese Patent Laid-open Publication 2001-185066 an electron beam apparatus where a sample is placed within a magnetic field formed in the vicinity of a magnetic pole positioned at the side of an electron source. The electron source-side magnetic pole is partitioned into a magnetic pole far from the sample and a magnetic pole close to the sample. The top surface of the magnetic pole far from the sample is positioned closer to the sample than an electrically insulating material provided between the magnetic pole far from the sample and the magnetic pole close to the sample. The magnetic field occurring between the magnetic pole far from the sample and the magnetic pole close to the sample is positioned in the vicinity of the part of the magnetic pole close to the sample that faces the sample. Magnetic flux can therefore be prevented from leaking and chromatic aberration coefficient Cc of a compound lens can be made smaller.
However, with the electron beam apparatus proposed in Japanese Patent Laid-open Publication 2001-185066, there is a problem in that the magnetic poles face each other and that discharges therefore occur at high-voltages of over 1 kV or more when the intervening gap is made too small. When the gap between the magnetic poles is made small in order to avoid this, another problem occurs in that a sub-magnetic field occurring as a result becomes large and it is therefore easy for the chromatic aberration coefficient Cc therefore to become large.
According to the present invention, in an electron beam apparatus having an electromagnetic field lens for focusing an electron beam onto a sample so as to irradiate the sample, an electromagnetic circuit of the electromagnetic field lens is provided with an upper magnetic pole far from the sample and a lower magnetic pole near to the sample, with electrical insulation being provided between the upper magnetic pole and the lower magnetic pole by a ferrite insulator provided between the upper side magnetic pole and the lower side magnetic pole in an integral manner with the magnetic poles so that the upper magnetic pole and the lower magnetic pole can be held at different potentials.